<p><b>(A)</b> Amino acid mutations resulting from five codon changes introduced into the UL37 gene of HSV-1 are indicated at top, along with the corresponding mutations of the previously described PRV R2 mutant and the respective positions of the mutations within a sequence alignment of nine alpha-herpesviruses (mutated positions highlighted in red). <b>(B)</b> Wild-type (WT) and R2-mutant (R2) HSV-1 single-step propagation kinetics were determined by counting plaque-forming units harvested from media and Vero epithelial cells (cells) at the times indicated. Viruses used in this study were not modified to encode a fluorescent tag. <b>(C)</b> Fluorescent plaque diameters of WT and R2-mutant HSV-1 encoding mCherry fused to the pUL25 capsid protein were compiled from three independent experiments and plotted as a percentage of the average WT plaque diameter. Error bars are s.d. (****, p < 0.0001 based on a two-tailed unpaired <i>t</i> test).</p>